Making an optic with a cladding

ABSTRACT

Embodiments related to making an optic comprising a cladding are disclosed. One example embodiment comprises forming a wedge-shaped light guide having opposing first and second faces and comprising a material having a first refractive index. The embodiment further comprises applying a cladding layer to the first face, and, applying an interface layer to the cladding layer. In this embodiment, the cladding layer has a second refractive index less than the first refractive index, and the interface layer has a third refractive index matched to the first refractive index.

BACKGROUND

A computer system may include one or more optical systems that providean image as output or receive an image as input. Example optical systemsinclude displays, cameras, scanners, and certain kinds oftouch-sensitive input systems. Some optical systems may include a lightguide that transmits an image to a touch-sensitive display surface,focuses an image on a detector, or does both. The light guide may bewedge-shaped, transparent in one or more visible and/or infraredwavelength ranges, and comprise at least one pair of opposing faces.Through the light guide, light of a certain wavelength range maypropagate laterally, via internal reflection from the opposing faces. Inmany cases, the material properties and overall configuration of thelight guide may affect the intensity and fidelity of the images providedby the optical system.

SUMMARY

Therefore, in one embodiment, a method for making an optic is provided.The method comprises forming a wedge-shaped light guide having opposingfirst and second faces and comprising a material having a firstrefractive index. The method further comprises applying a cladding layerto the first face, and, applying an interface layer to the claddinglayer. In this embodiment, the cladding layer has a second refractiveindex less than the first refractive index, and the interface layer hasa third refractive index matched to the first refractive index.

It will be understood that the summary above is provided to introduce insimplified form a selection of concepts that are further described inthe detailed description, which follows. It is not meant to identify keyor essential features of the claimed subject matter, the scope of whichis defined by the claims that follow the detailed description. Further,the claimed subject matter is not limited to implementations that solveany disadvantages noted above or in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows aspects of an example computer system in one embodiment inaccordance with the present disclosure.

FIG. 2 is a schematic, cross-sectional view showing aspects of opticalsystem 14 in one embodiment in accordance with the present disclosure.

FIGS. 3 and 4 show aspects of an example wedge-shaped light guide in oneembodiment in accordance with the present disclosure.

FIG. 5 shows a multilayer turning structure in one embodiment inaccordance with the present disclosure.

FIG. 6 shows transmission and reflection spectra of a dichroic coatingapplied to a polymethylmethacrylate light guide in accordance with oneembodiment of the present disclosure.

FIGS. 7, 8, and 9 show ray diagrams in which light interacts with animaging optic in accordance with one embodiment of the presentdisclosure.

FIG. 10 shows graphs of transmission efficiency versus incidence anglefor selected interfaces in example embodiments in accordance with thepresent disclosure.

FIG. 11 shows aspects of an example input device in one embodiment inaccordance with the present disclosure.

FIG. 12 is a schematic, cross-sectional view showing aspects of anoptical system and an input zone of an input device in one embodiment inaccordance with the present disclosure.

FIG. 13 shows another multilayer turning structure in one embodiment inaccordance with the present disclosure.

FIGS. 14 and 15 show ray diagrams in which light interacts with adisplay optic in accordance with one embodiment of the presentdisclosure.

FIG. 16 shows graphs of transmission efficiency versus incidence anglefor selected, interfaces in example embodiments in accordance with thepresent disclosure.

FIG. 17 shows a ray diagram in which light interacts with a displayoptic in accordance with one embodiment of the present disclosure.

FIG. 18 illustrates an example method for making an imaging or displayoptic in one embodiment in accordance with the present disclosure.

FIG. 19 illustrates an example method for making an imaging or displayoptic in one embodiment in accordance with the present disclosure.

FIG. 20 shows an example application system to enable a cladding to beapplied to a wedge-shaped light guide in accordance with one embodimentof the present disclosure.

DETAILED DESCRIPTION

The subject matter of the present disclosure is now described by way ofexample and with reference to certain illustrated embodiments.Components that may be substantially similar in two or more embodimentsare identified coordinately and are described with minimal repetition.It will be noted, however, that components identified coordinately indifferent embodiments of the present disclosure may be at least partlydifferent. It will be further noted that the drawings included in thisdisclosure are schematic. Views of the illustrated embodiments aregenerally not drawn to scale, and the aspect ratio of some drawings maybe purposely distorted to make selected features or relationships easierto see.

FIG. 1 shows aspects of an example computer system 10 in one embodiment.The computer system includes a large-format, touch-sensitive displaysurface 12. Optical system 14, located below the touch-sensitive displaysurface, may be configured to provide both display and inputfunctionality for the computer system. Accordingly, FIG. 1 showscontroller 16 operatively coupled to the optical system. The controllermay be any device configured to provide display data to and receiveinput data from the optical system. In some embodiments, the controllermay comprise all or part of a computer; in other embodiments, thecontroller may be any device operatively coupled to a computer via awired or wireless communications link.

To provide display functionality, optical system 14 may be configured toproject a visible image onto the touch-sensitive display surface. Toprovide input functionality, the optical system may be configured tocapture at least a partial image of objects placed on thetouch-sensitive display surface—fingers, electronic devices, papercards, food, or beverages, for example. Accordingly, the optical systemmay be configured to illuminate such objects and to detect the lightreflected from the objects. In this manner, the optical system mayregister the position, footprint, and other properties of any suitableobject placed on the touch-sensitive display surface.

FIG. 2 is a schematic, cross-sectional view showing aspects of opticalsystem 14 in one embodiment. The optical system includes backlight 18,imaging optic 20, light valve 22, and diffuser 24. The backlight andlight valve may be operatively coupled to controller 16 and configuredto provide a visual display image to touch-sensitive display surface 12.

Backlight 18 may be any illuminant configured to emit visible light.Light from the backlight (light ray 26, for example) is projectedthrough imaging optic 20 and is modulated with respect to color andintensity by numerous light-gating elements of light valve 22. In someembodiments, the light valve may comprise a liquid-crystal displaydevice, but other light-modulating devices may be used as well. In thismanner, the backlight and the light valve may together create a displayimage. The display image is projected through diffuser 24 and is therebyprovided to touch-sensitive display surface 12. To ensure adequatedisplay-image intensity, the imaging optic and the diffuser may beconfigured to transmit a substantial portion of the visible lightincident upon them, at least in a direction normal to thetouch-sensitive display surface, from which direction the display imagewould typically be viewed.

In the embodiment shown in FIG. 2, imaging optic 20 compriseswedge-shaped light guide 27 having an upper face 28 and a lower face 30.FIG. 3 illustrates one example wedge-shaped light guide in greaterdetail. It will be understood, however, that no aspect of FIG. 3 isintended to be limiting, because numerous wedge-shaped light guidevariants are contemplated.

Referring now to FIG. 3, the opposing upper and lower faces of thewedge-shaped light guide may, in some embodiments, be substantiallyplanar and nearly parallel, but offset from each other by a wedge angleof 1° or less. In one specific embodiment, the wedge angle may be 0.72degrees, for example. As used herein, a ‘substantially planar’ surfaceis one that broadly conforms to a plane when surface roughness andmanufacturing anomalies are not considered. For example, in one specificembodiment, a substantially planar surface may have a roughness of 3nanometers (roughness average) or less. The wedge-shaped light guide maybe oriented symmetrically with respect to the horizontal and/or anyplane parallel to touch-sensitive display surface 12. Therefore, theangle of intersection between the upper or lower face of the light guideand any plane parallel to the touch-sensitive display surface may beone-half the wedge angle. Accordingly, the phrases ‘normal to thewedge-shaped light guide,’ ‘normal to the imaging optic,’ and ‘normal tothe opposing faces,’ etc., are used herein to indicate an orientationsubstantially normal to the touch-sensitive display surface.

Wedge-shaped light guide 27 has a thinner side 32, and a thicker side 34opposite the thinner side. In the example illustrated in FIG. 3, thewedge-shaped light guide is milled on the thicker side to define asection of a sphere enclosed by an acute central angle. The radius ofcurvature of the section so defined may be determined based on thedetailed configuration of optical system 14, in which the wedge-shapedlight guide is to be installed. In one particular embodiment, thethicker side is approximately twice the thickness of the thinner side,and the radius of curvature of the thicker side is approximately twicethe length of the wedge-shaped light guide. In some embodiments, one ormore sides of the wedge-shaped light guide (e.g., thinner side 32 orthicker side 34) may function as a lens, wherein the radius of curvaturedefines a focal length of the lens.

A more detailed sectional view of thicker side 34 in one, non-limitingembodiment is shown in FIG. 4. The drawing shows an array ofsubstantially planar facets 36 running horizontally along the thickerside of the wedge-shaped light guide. The facets define a series ofhorizontal ridges that extend to meet the upper and lower edges of thethicker side. The facets may be coated with a reflective material toform an interleaved reflector on the thicker side. The interleavedreflector so formed may serve various functions in the optical system inwhich the light guide is to installed—directing an image from aprojector or onto a detector, for example. In one, non-limiting example,twenty-seven facets may be formed in the thicker side of thewedge-shaped light guide, forming a series of horizontal ridges spacedabout 840 microns apart and extending about 80 microns from an upper orlower edge of the thicker side. In other examples, the thicker side ofthe wedge-shaped light guide may have any other suitable shape orprofile. Based on a wedge-shaped light guide as described herein,imaging optic 20 may be configured to transmit light laterally betweenthe opposing first and second faces at least partly via total internalreflection from a boundary of the wedge-shaped light guide. It will beunderstood, of course, that the details of the configuration describedhere and in FIG. 3 are presented for the purpose of example, and are notintended to be limiting in any manner.

Returning now to FIG. 2, optical system 14 may be further configured toprovide input functionality to computer system 10. Accordingly, theillustrated optical system includes detector 38. The detector may be acamera—an infrared-sensitive, digital camera, for example. Imaging optic20 may be configured to direct onto the detector light from one or moreobjects arranged on or contacting touch-sensitive display surface 12.Such light may originate from various sources, as described hereinafter.Accordingly, the detector may capture at least a partial image of theone or more objects.

FIG. 2 shows object 40 in contact with touch-sensitive display surface12, and light ray 42 propagating away from the object. The illustratedlight ray is shown passing through various components of optical system14 and into imaging optic 20. To image light from the touch-sensitivedisplay surface onto detector 38, the imaging optic may be configured toturn the light towards the reflective thicker end of the wedge-shapedlight guide and to confine the turned light en route to the detector viatotal internal reflection. Accordingly, lower face 30 of the imagingoptic comprises multilayer turning structure 44. The present disclosureembraces numerous variants of the multilayer turning structure. Forexample, the multilayer turning structure may be reflective, so thatlight is directed back through wedge-shaped light guide 27.

FIG. 5 shows a more detailed view of multilayer turning structure 44 inone embodiment. The multilayer turning structure includes base layer 46.In some embodiments, the base layer may be a 300 micron-thick layer ofpolyethylene tetraphthalate (PET), for example. In other embodiments,the base layer may comprise any other suitable material at any suitablethickness. On top of the base layer is disposed a patterned layer 48having a regular prismatic structure in which one face of each prism isorthogonal to the base layer, and an adjacent face is oriented obliqueto the base layer. The adjacent face oriented oblique to the base layermay be oriented between 15 and 45 degrees from the base layer—28degrees, for example. The patterned layer may comprise an acryliccopolymer, for example, among various other suitable materials. In oneembodiment, base layer 46 and patterned layer 48 may be provided in theform of a commercially prefabricated, multilayer film. For example, animage-directing film (IDF) manufactured by 3M Corporation of Saint Paul,Minn. is one example of a suitably configured, two-layer film that maybe used for the base layer and the patterned layer. On top of thepatterned layer, a reflective or partly reflective coating may bedisposed. In the embodiment illustrated in FIG. 5, the reflective orpartly reflective coating comprises dichroic coating 50.

Dichroic coating 50 may comprise a plurality of very thin dielectriclayers applied to patterned layer 48 in any suitable manner. In oneembodiment, the dichroic coating may be applied via evaporation orsputtering of various inorganic oxides or other materials onto thepatterned layer, by chemical vapor deposition, or in any other suitablemanner. In one embodiment, the thin dielectric layers may be quarterwave coatings of alternating high and low refractive indices—six toeight layers, for example.

Taken together, base layer 46, patterned layer 48, and dichroic coating50 comprise turning film 52 in one example embodiment. In some examples,one or more constituents of the turning film may be chosen to have acoefficient of thermal expansion similar to that of the wedge-shapedlight guide, such that nominal temperature variations do not cause theturning film to deform or separate from the wedge-shaped light guide. Asdescribed hereinafter, the turning film may be prepared separately andbonded to the remaining layers of the multilayer turning structure viaan interface layer. Further, in some embodiments, the interface layermay comprise a layer of adhesive. Accordingly, in the embodimentillustrated in FIG. 5, adhesive layer 54 is disposed on the turningfilm. The adhesive layer may be a polyacrylic and/or ultraviolet-curableadhesive, for example, such as Dymax 3091 or Dymax 3099, available fromthe Dymax Corporation of Torrington, Conn. The adhesive layer serves tobond the turning film to cladding layer 56, which is described infurther detail below. In other embodiments fully consistent with thisdisclosure, a prismatic patterned layer may be sealed in an encapsulantlayer and then bonded to the wedge-shaped light guide using a transferadhesive, such as Product 8154 of Adhesives Research, Inc., of GlenRock, Pa. It will be understood that a dichroic coating may be includedin some turning films and omitted in others. The dichroic coating may beomitted, for example, in embodiments where the imaging or display opticis not configured to separate visible light from infrared light, or doesso in a different manner. In turning films that lack a dichroic coating,a broadband reflective coating may be substituted, as further describedbelow.

Continuing in FIG. 5, cladding layer 56 comprises a thin layer ofmaterial. In some embodiments, the cladding layer may be applied as acoating on wedge-shaped light guide 27, as described hereinafter. Thematerial or materials comprising the cladding layer may be chosen inview of certain physical properties. First, the cladding layer, at leastin the thickness ranges set forth below, may be substantiallynon-absorbing and substantially non-scattering to light that imagingoptic 20 is configured to transmit. Second, the cladding layer may besubstantially resilient to expansion and compression strain, such thatnominal temperature variations do not cause the cladding layer to crackor separate from the wedge-shaped light guide. Third, the cladding layermay have a lower refractive index than the material from which thewedge-shaped light guide is formed. For example, if the wedge-shapedlight guide has a refractive index of 1.492, the cladding layer may havea refractive index in the range 1.1 to 1.4. Specific examples ofmaterials that may be used for the cladding layer include, but are notlimited to, silicone polymers (n˜1.38) and fluoropolymers (n˜1.33).Accordingly, in some specific embodiments, the cladding layer maycomprise Teflon AF (El DuPont de Nemours & Co. of Wilmington, Del.),Cytop (Asahi Corporation of Tokyo, Japan), MY-133 (MY PolymersCorporation of Rehovot, Israel), or LS-233 (Nusil Corporation ofCarpinteria, Calif.), as examples. In other embodiments, the claddinglayer may comprise a moth-eye layer, e.g., a layer of material having arefractive index typical of optical materials (e.g., acrylic, n˜1.492),but incorporating an array of sub-wavelength features containing air.The result is a layer having a lower effective refractive index.Microporous materials such as aerogels and foams contain randomizedpockets of air and can serve the same function, provided that the airpockets are substantially smaller than the wavelength of interest.Fourth, the cladding layer may have a lower refractive index than thematerial from which the interface layer is formed—adhesive layer 54 inthis example. Accordingly, the refractive index of the interface layermay, in some embodiments, be matched to that of the wedge-shaped lightguide. As used herein, refractive indices are ‘matched’ if they differby no more than ±2%. By virtue of the relative refractive indices of thecladding layer and the wedge-shaped light guide, the imaging optic maybe configured to transmit light laterally between the opposing first andsecond faces of the wedge-shaped light guide at least partly via totalinternal reflection from a boundary of the cladding layer—lower face 30,in the illustrated embodiment.

Multilayer turning structure 44 is configured to interact minimally withthe light passing through the imaging optic from backlight 18 (light ray26, for example); interaction is averted because dichroic coating 50 issubstantially transparent to visible light and because light projectedfrom the backlight intersects the various interfaces of the multilayerturning structure at too small an angle (measured normal to theboundary) to undergo total internal reflection. FIG. 6 showstransmission and reflection spectra of the dichroic coating applied tothe patterned side of an IDF film; percent transmittance/reflectance isplotted on the vertical axis, and wavelength in nanometers is plotted onthe horizontal. The transmission spectrum (the dashed curve) reveals arelatively high transmittance in the visible wavelength range of roughly450 to 700 nm. Further, the ray diagram of FIG. 7 illustrates thatvisible light intersecting the multilayer turning structure at asuitably low incidence angle (light ray 26, for instance) will passdirectly through the structure.

In contrast, multilayer turning structure 44 may interact significantlywith infrared light (light ray 42, for example) from the one or moreobjects disposed on touch-sensitive display surface 12. Strongerinteraction with infrared light is a consequence of dichroic coating 50being substantially reflective to infrared light, as shown by thereflectance spectrum (dot-dashed curve) in FIG. 6.

FIG. 8 shows light ray 42, for example, entering imaging optic 20 at anangle less than the Snell's Law critical angle for any boundary throughwhich it passes. As a result, substantially all of the light isrefracted through wedge-shaped light guide 27, cladding layer 56, andadhesive layer 54. Because dichroic coating 50 is reflective to infraredlight, the light ray is turned towards detector 38. Thus, FIG. 8 showsturned light ray 58 incident upon cladding layer 56.

In order for any light from object 40 to be imaged on detector 38, thelight must enter imaging optic 20 via refraction through one or moreinterfaces. At each boundary, however, reflection will also occur. Thus,FIG. 8 shows turned light ray 58 splitting into refracted light ray 60and reflected light ray 62. Refracted light ray 60 is further split intoforward light ray 64 and an interfering light ray 66. In the embodimentillustrated in FIG. 8, the equivalent refractive indices of adhesivelayer 54 and wedge-shaped light guide 27 may help to provide that theintensity of interfering light ray 66 is nearly equal to that ofreflected light ray 62. Further, the phase angle separating the two raysis determined by the thickness of cladding layer 56 and by the angle atwhich turned light ray 58 intersects the cladding layer. If the phaseangle is π M, where M is any odd integer, then the two light raysinterfere destructively, thereby eliminating the reflected power andmaximizing the forward power. As described herein, the thickness of thecladding layer may be chosen to provide such a phase angle. In thismanner, the imaging optic may be configured to attenuate a reflection oflight which is incident on a boundary of the cladding layer at an angleless than a Snell's Law critical angle for the boundary (the anglemeasured normal to the boundary). In particular, to attenuate lighthaving a median wavelength λ, the thickness d of the cladding layer maybe selected so that the optical path through the cladding layer isapproximately one-half of the median wavelength:d≈λ/[2 n₂ cos(θ)],   (equation 1)where n₂ is the refractive index of the cladding material, and θ is thepropagation angle relative to the interface normal. In one example, ifthe propagation angle is 70 degrees, the wavelength 850 nm, and therefractive index of the cladding layer is 1.33, the thickness of thecladding layer may be 1.9 μm. In other examples, the thickness of thecladding layer may be any odd-integer multiple of the value d definedabove: 3 d, 5 d, 7 d, for instance. Equation 1 is valid for any range ofpropagation angles below θ_(c), the Snell's Law critical angle for totalinternal reflection at the interface between the wedge-shaped lightguide and the cladding layer, viz.,θ_(c)=arcsin(n₂/n₁),   (equation 2)where n₁ is the refractive index of the material of which thewedge-shaped light guide is made. However, for the purpose of selectinga suitable cladding layer thickness, the value of θ in equation 1 may beset to θ_(c). Thus, example cladding-layer thicknesses may included≈Mλ/[2 n₂ cos(θ_(c))],   (equation 3)where M is any odd integer. Therefore, in one, non-limiting embodiment,

$\begin{matrix}{d \approx \frac{M\;\lambda}{2n_{2}\sqrt{1 - \left( {n_{2}/n_{1}} \right)^{2}}}} & \left( {{equation}\mspace{14mu} 4} \right)\end{matrix}$In these examples, the thickness tolerance may be ±10 percent or ±5percent, for example.

On penetrating wedge-shaped light guide 27, forward light ray 64 mayreach upper face 28 at greater than the Snell's Law critical angle andbe reflected back to lower face 30. At this point, shown in FIG. 9, theforward light ray may now intersect cladding layer 56 at greater thanthe critical angle and be internally reflected towards detector 38.After numerous internal reflections, light from object 40 may exit theimaging optic and be imaged by the detector.

To better appreciate some of the advantages of the illustratedembodiment, it is helpful to consider an otherwise similar configurationin which no cladding layer is disposed on wedge-shaped light guide 27.For instance, an air space could be disposed between the wedge-shapedlight guide and a suitable turning structure. Such a configuration mayenable the basic functionality described above, but may suffer at leastthree, interrelated problems. First, significant image intensity may belost due to reflection as the light enters the wedge-shaped light guidefrom the turning structure. Such attenuation may decrease thesignal-to-noise ratio for image detection. In particular, light from theturning structure, instead of undergoing the destructively interferingreflections described above, may undergo a single, intensity-stealingreflection at the lower boundary of the light guide. As a result,significant forward power may be lost, thereby reducing the intensity ofthe image provided to the detector. Second, the attenuation of theforward light ray may be sensitive to the polarization state of theincident light. This effect may result in undesirable variations inimage intensity depending on the geometric and materials properties ofthe objects being imaged. Third, if the reflected light should somehowre-enter the light guide at a different location or incidence angle, thedetector may register a ghost image superposed on the desired image.

Providing a cladding layer 56 of controlled thickness sandwiched betweentwo higher-index regions addresses each of the deficiencies identifiedabove. The advantages this structure feature provides are furtherunderscored with reference to FIG. 10, which shows two graphs oftransmissivity through a light guide boundary as a function of incidenceangle. Upper graph 68 is for an unclad light guide (PMMA, n=1.49); lowergraph 70 is for the same light guide clad with a ca. 3.5wavelength-thick layer of Nusil LS2233 (n=1.33), and a layer of acrylicadhesive (n=1.49) disposed over the cladding layer. Transmissivity wasprobed using 550 nm light of S and P polarization states. It is clearfrom these graphs that the sandwiched cladding layer increases overalltransmissivity by reducing reflectivity, and further reduces thepolarization sensitivity of the transmissivity relative the unclad lightguide boundary.

As noted above, light from one or more objects disposed on thetouch-sensitive display surface may originate from various sources. Inone embodiment, the light may be emitted by the objects. In theembodiment illustrated in FIG. 2, however, the light is provided bydiffuse illumination of the objects, and reflected back through thetouch-sensitive display surface. Thus, FIG. 2 shows infrared emitters72—infrared light-emitting diodes, for example—and illuminating lightguide 74. In the configuration illustrated in FIG. 2, the illuminatinglight guide is configured to illuminate the one or more objects frombehind the touch-sensitive display surface. The illuminating light guidemay be any optic configured to admit infrared light from one or moreentry zones 76 and to project at least some of the infrared light fromexit zone 78. The entry and exit zones of the illuminating optic mayeach comprise a turning film or other turning structure. In order toadmit light from the infrared emitters and simultaneously provide thedesired light-turning function, the turning structures associated withthe entry zone and the exit zone may be oriented differently from eachother. Further, the exit zone may comprise a low-angle diffuser film,such as product ADF-0505 manufactured by FusionOptix of Woburn, Mass.The low-angle diffuser film may be included in order to couple out thelight incident on display surface 12 at a grazing angle, so it is notimaged by imaging optic 20. More specifically, light from the LED arraymay be trapped by TIR in the illuminating light guide; weak diffusion bythe low-angle diffuser film causes the ray angles to be scattered withinthe illuminating light guide. At each interaction, some light passes theTIR angle and escapes. Although the light may escape half from the topand half from the bottom, only the light escaping from the top is usedto illuminate objects.

FIG. 2 shows infrared light ray 80, for example, entering illuminatinglight guide 74 through entry zone 76, being turned via a turningstructure of the entry zone, and undergoing an internal reflection at aboundary of the illuminating light guide. The internal reflection is aconsequence of the illustrated light ray intersecting the boundary at anangle greater than the Snell's Law critical angle. Continuing forward,the illustrated light ray interacts with the turning structure of exitzone 78, and is reflected substantially upward from the exit zone. Atleast some of the illustrated light ray is now transmitted through theboundary of the illuminating light guide, instead of being totallyinternally reflected; this is because the illustrated light ray nowintersects the boundary at an angle less than the critical angle.

In the embodiment illustrated in FIG. 2, exit zone 78 of illuminatinglight guide 74 is planar and substantially parallel to touch-sensitivedisplay surface 12. In this configuration, light projected from the exitzone passes through diffuser 24 and may illuminate object 40, which isin contact with the touch-sensitive display surface. It will beunderstood however, that numerous other illumination configurations arepossible, and are equally consistent with the present disclosure.

FIG. 11 shows aspects of an example input device 82 in one embodiment.The input device includes input zone 84, where user input is received.User input may be received via a touch-sensitive area of the input zone(a virtual keypad, mouse pad, or control pad, for example), and/or amechanical keyboard. Optical system 86, located behind the input zone,may be configured to provide input and/or input-guiding functionality tothe input zone. Accordingly, the optical system is operatively coupledto controller, indicated schematically at 1116. While FIG. 11 shows thecontroller outside of the input device (e.g., such that the input deviceis controlled by a computing device to which the input device isattached), it will be understood that the controller may be integratedinto the input device in embodiments equally consistent with thisdisclosure. In one embodiment, the optical system may be configured toilluminate all or part of the input zone and to detect light reflectedfrom objects placed on the input zone, substantially as describedhereinabove with reference to touch-sensitive display surface 12. Inother embodiments, however, the input functionality of the input zonemay be enabled independent of the optical system—via a capacitive orresistive touch screen and/or mechanical key switches, for example.

In the embodiment shown in FIG. 11, input zone 84 includes image-adaptedarea 88. The image-adapted area is an area on which one or morechangeable images—keyfaces, dials, slide-bar controls, etc.—may bedisplayed for the purpose of guiding user input. Accordingly, opticalsystem 86 may be configured to display one or more changeable images onthe image-adapted area, and thereby provide input-guiding functionalityto the input zone. In other embodiments equally consistent with thisdisclosure, the image-adapted area may occupy multiple, non-overlappingregions of the input zone, or it may coincide with the entire inputzone.

FIG. 12 is a schematic, cross-sectional view showing aspects of opticalsystem 86 and input zone 84 in one embodiment. The optical systemincludes side-mounted light source 89, display optic 1220, and lightvalve 1222; the input zone includes partly transparent keyface 90disposed within image-adapted area 88.

As in the previous embodiments, the light valve may be anyimage-forming, light-gating device—a liquid-crystal display device, forexample. Side-mounted light source 89 may be any illuminant configuredto provide suitably intense, divergent light over a suitably broadvisible wavelength range. In the embodiment illustrated in FIG. 12,light from the side-mounted light source (light ray 91, for example) isprojected through display optic 1220 and is modulated by numerouslight-gating elements of light valve 1222 to provide a modulated imageto image-adapted area 88, and specifically, to keyface 90.

Taken together, side-mounted light source 89 and light valve 1222constitute an image-creating subsystem in one example embodiment. Theimage-creating subsystem may be adapted to create a changeable, visibleimage using light from a light source (side-mounted light source 89, forexample) and to provide the changeable, visible image to keyface 90 orelsewhere within image-adapted area 88. Accordingly, the image-creatingsubsystem may be operatively coupled to controller 1116. Further,display optic 1220 may be configured to turn and project the light fromthe light source so that the visible image may be displayed on keyface90, or elsewhere within the image-adapted area. In the embodiment shownin FIG. 12, display optic 1220 is configured to direct the visible lightthrough the light valve and onto the image-adapted area.

In other embodiments equally consistent with this disclosure,image-creating subsystems of other configurations may be used instead.For example, a light valve may be incorporated into a side-mounted lightsource so that a fully formed image is projected through display optic1220 and onto image-adapted area 88. In still other examples, the imagemay created via a laser operatively coupled to controller 1116 andconfigured to raster coherent, image-modulated light into the displayoptic.

In the embodiment illustrated in FIG. 12, it is assumed that inputfunctionality is provided independent of optical system 86—via acapacitive or resistive touch screen and/or mechanical key switches, forexample. Therefore, no detector or other input-receiving device isincluded in the drawing. However, in some embodiments fully consistentwith this disclosure, the optical system may be further configured toprovide input functionality as well, as described previously in thecontext of optical system 14.

To provide an image to image-adapted area 88, display optic 1220 may beconfigured to transmit light via total internal reflection and to turnat least some of the light towards the image-adapted area. Therefore,the display optic comprises wedge-shaped light guide 1227, having anupper face 1228 and a lower face 1230. Multilayer turning structure 1244is disposed on the lower face. In the illustrated embodiment, thewedge-shaped light guide further includes a thicker side adjacent theupper and lower faces and supporting a reflective coating 92, and, athinner side adjacent the upper and lower faces, opposite the thickerside. Coupled to a display optic of this configuration, theimage-creating subsystem may be adapted to project light for forming theimage into the thinner side of the wedge-shaped light guide.

FIG. 13 provides a more detailed view of multilayer turning structure1244. In one embodiment, multilayer turning structure 1244 may besubstantially the same as multilayer turning structure 44 describedhereinabove, but numerous variations are contemplated as well. Forexample, in embodiments where transmission of light normal to thedisplay optic is not an issue, dichroic coating 50 of the previousembodiment may be replaced by a broadband reflective coating.Accordingly, the embodiment illustrated in FIG. 13, shows broadbandreflective coating 93 disposed on top of patterned layer 1348. In oneembodiment, the broadband reflective coating may be a thin layer ofaluminum. In another embodiment, it may be a thin film of silverdisposed on top of an inconel sublayer. It will be understood that theexamples provided herein are not intended to be limiting, as variousother reflective coatings may be suitable as well. In contrast to theprevious embodiments, multilayer turning structure 1244 is configured tointeract strongly with light over a broad wavelength range that includesvisible and infrared regions.

FIG. 14 shows light ray 91 entering display optic 1220 at an anglegreater than the Snell's Law critical angle for the boundary between thewedge-shaped light guide 1227 and cladding layer 1356; the light ray istotally internally reflected. On reaching upper face 1228, the light rayis further reflected back to lower face 1230. As shown in FIG. 15, lightray 91 may now intersect the boundary between the wedge-shaped lightguide and the cladding layer at less than the critical angle and berefracted out of the light guide. The light ray then reflects offbroadband reflective coating 93, projects upward through the displayoptic, and forms an image on image-adapted area 88—and on keyface 90 inparticular.

In order for any light reflected from side-mounted light source 89 toreach image-adapted area 88, it may exit wedge-shaped light guide 1227via refraction. However, reflection will also occur at each boundarythat the light ray intersects. Thus, FIG. 15 shows light ray 91splitting into a refracted light ray 1560 and a reflected light ray1562. Refracted light ray 1560 is further split into a forward light ray1564 and an interfering ray 1566. In the embodiment illustrated in FIG.15, the equivalent refractive indices of adhesive layer 1354 andwedge-shaped light guide 1227 may help to provide that the intensity ofinterfering light ray 1566 is nearly equal to that of reflected lightray 1562. Further, the phase angle separating the two rays is determinedby the thickness of cladding layer 1356 and by the angle at which lightray 91 intersects the cladding layer. The thickness of the claddinglayer may therefore be chosen, as previously described, to eliminate thereflected power and to maximize the forward power.

As in the case of the previous embodiment, the advantages of the presentembodiment are best understood with reference to an otherwise similarconfiguration in which no cladding layer is disposed on the wedge-shapedlight guide. Such a configuration would suffer an analogous, thoughoptically converse, set of problems. First, residual internal reflectionbelow the critical angle of incidence would cause a significant amountof light to remain in the wedge-shaped light guide, and thereby stealintensity from the exiting, forward light ray. As a result, theintensity of the image projected on image-adapted area 88 would beattenuated. Second, the attenuation would be sensitive to thepolarization state of the incident light, resulting in variations inimage intensity depending on geometric and materials properties of theoptical system. Third, the residual internal reflection noted abovewould cause the light remaining in the light guide to go an extra bouncebefore exiting, thereby forming a ghost image superposed on the desiredimage.

By providing cladding layer 1356 on display optic 1220, the illustratedembodiment addresses each of the deficiencies identified above.

As shown in FIG. 10, both clad and unclad light guides exhibit totalinternal reflection of light incident on the light-guide boundary abovea critical angle, and refract at least some light incident on theboundary below the critical angle. For a light guide having a thin-layercoating, however, the critical angle may depend on wavelength. In caseswhere the propagating light is confined to a narrow wavelengthband—light from an IR-LED, for example—this issue may not pose asignificant issue. However, in applications where a light guide is usedto image broad-band light, a wavelength dependence on the critical anglemay lead to various undesired effects, including color distortion andprojection of superposed, false-color images. Fortunately, the claddinglayers as disclosed herein are found to be suitably insensitive towavelength, as shown in the transmission spectra of FIG. 16, wheretransmission efficiency is plotted on the vertical axis, and incidenceangle is plotted on the horizontal for wavelengths in the visible.

In other embodiments, the thin-layer cladding approach as describedhereinabove may be taken a step further. In a display optic comprising awedge-shaped light guide having opposing upper and lower faces, acladding layer may be disposed on the lower face, as describedhereinabove, and on the upper face as well. A potential advantage ofthis embodiment is now described with reference to the ray diagram ofFIG. 17.

The layered structure of the display optic shown in FIG. 17 is similarto the one shown in FIGS. 14 and 15, but further includes upper claddinglayer 94 and capping layer 95. The appropriate composition and thicknessof the upper cladding layer may be substantially the same as that ofcladding layer 56, described hereinabove. However, the upper claddinglayer may be chosen to have a refractive index lower than that ofcladding layer 1756 of the presently described embodiment. The cappinglayer may comprise any suitably transparent material having a refractiveindex matched to that of wedge-shaped light guide 1727.

FIG. 17 shows light ray 91 intersecting the boundary betweenwedge-shaped light guide 1727 and cladding layer 1756 at less than thecritical angle for the boundary. Most of the light is thereforerefracted out of the light guide, where it reflects off broadbandreflective coating 1793 and projects upward through the display optic toform an image.

As indicated above, reflection will also occur at each boundary that thelight ray intersects. Thus, FIG. 17 shows light ray 91 splitting into arefracted light ray 1760 and a reflected light ray 1762. Refracted lightray 1760 is further split into a forward light ray 1764 and aninterfering ray 1766. In the embodiment illustrated in FIG. 17, theequivalent refractive indices of adhesive layer 1754 and wedge-shapedlight guide 1727 provide that the intensity of interfering light ray1566 is nearly equal to that of reflected light ray 1562. Further, thephase angle separating the two rays is determined by the thickness ofcladding layer 1756 and by the angle at which light ray 91 intersectsthe cladding layer. The thickness of the cladding layer may therefore bechosen, as described above, to attenuate the reflected power and tocorrespondingly increase the forward power.

As further indicated above, destructive interference between reflectedlight ray 1762 and interfering light ray 1766 may reduce the power ofthe reflected ray to a small fraction of the forward ray (10%, forexample), but reflection at this level may still be problematic forsome, select applications. Therefore, FIG. 17 shows reflected light ray1762 incident on the boundary between wedge-shaped light guide 1727 andupper cladding layer 94. The reflected light ray now splits intoreturning light ray 96 and refracted light ray 97. Refracted light ray97 further splits into escaping light ray 98 and interfering light ray99. The equivalent refractive indices of capping layer 95 andwedge-shaped light guide 1727 may help to provide that the intensity ofreturning interfering light ray 97 is nearly equal to that ofinterfering returning light ray 99. Further, the phase angle separatingthe two rays is determined by the thickness of upper cladding layer 94and by the angle at which light ray 91 intersects the upper claddinglayer. The thickness of the upper cladding layer may therefore bechosen, as described above, to eliminate the returning power and tomaximize the escaping power. Accordingly, this embodiment provides notone but two stages of destructive interference, the effect of which isto further reduce the intensity of ghost images projected through thedisplay optic.

FIG. 18 illustrates an example method 100 for making an imaging ordisplay optic in one embodiment. The method begins at 102, where awedge-shaped light guide having opposing upper and lower faces isformed. The wedge-shaped light guide may be formed in any suitablemanner. One example method 104 for forming the wedge-shaped light guideis illustrated in FIG. 19.

Method 104 begins at 106, where a molten, thermoplastic polymer or otherthermoplastic material is forced through an extrusion die having aquadrilateral or other suitable cross section. The thermoplastic polymermay comprise a polyacrylate, a polyacrylonitrile, a polyamide, and/or apolycarbonate, for example. The thermoplastic material may be selectedfor transparency in one or more visible, ultraviolet, and/or infraredwavelength ranges. In embodiments where the light guide is to be usedsolely for displaying and/or collecting optical images, transparencyover the visible range may be sufficient. In other embodiments, however,the thermoplastic polymer may be selected for transparency in variousinfrared and/or ultraviolet ranges as well. Further, the thermoplasticmaterial may be chosen in view of its refractive index. In someembodiments, the thermoplastic material, in solid form, may have arefractive index greater than 1.4.

Forcing the molten thermoplastic polymer through a die having aquadrilateral cross-section gives rise to a substantially wedge-shapedextrusion having a pair of opposing faces and a quadrilateralcross-section. In other embodiments, the die may be shaped differently,thereby providing a differently shaped extrusion. For example, theextrusion die may be rectangular in shape and give rise to a sheet-like(i.e., rectangular prismatic) extrusion.

Continuing in FIG. 19, method 104 advances to 108, where the cooledextrusion is cut to one or more fixed dimensions, including but notlimited to a fixed width. The extrusion may be cut by using a saw or amill. The dimensions to which the extrusion is cut may be chosen basedon the dimensions of the display device in which the light guide is tobe installed.

Method 104 advances to 110, where the cut extrusion is refined to anappropriate shape and to appropriate dimensions for further processing.In some embodiments, the appropriate shape may be similar to the finalshape of the light guide that is desired, and the appropriate dimensionsmay be the same as or slightly larger than the desired final dimensions.Refining the extrusion may comprise machining, cutting, milling,etching, and/or polishing, as examples. Etching may comprise wet or drymechanical etching (e.g., sanding or filing) and/or chemical etching.Any etching process may be conducted with the aid of a mask (e.g., aphotomask) to vary the etching depth in a controllable manner, tointroduce surface features, etc.

Refining the extrusion at 110 may also comprise modifying across-section of the extrusion. Thus, in some embodiments, process step106 may result in an extrusion having the desired wedge shape, while inother embodiments, the extrusion may have a rectangular, sheet-likeshape before refinement, and at 110, be refined to have the desiredwedge shape.

In order for the wedge-shaped light guide to transmit images with highfidelity and without undue loss, the opposing faces may be configured tobe flat and smooth. In some embodiments, the methods describedhereinabove may yield surfaces having adequate smoothness. In otherembodiments, however, refinement at 110 may further comprise finelyadjusting the dimensions of the wedge-shaped light guide until thedesired planarity and smoothness is achieved. The dimensions may befinely adjusted via mechanical etching or polishing, as described above,via compression molding, or in any other suitable manner.

Returning now to FIG. 18, method 100 advances to 112, where a thincladding layer is applied to at least a first face of the wedge-shapedlight guide. The thin cladding layer applied according to this methodmay have substantially the same properties as described for claddinglayers 56, 1356, and/or 1756 of the embodiments described hereinabove.It will be understood, however, that the cladding layer appliedaccording to this method may also be at least partly different. Thus,the cladding layer may have a refractive index less than that of thewedge-shaped light guide. The refractive index may be less than 1.4, forexample. Further, the thickness of the cladding layer may be selectedbased on the wavelength range of the light to be imaged and/or displayedas described hereinabove with reference to equation 1 and thedescription following equation 1.

In some embodiments, applying the cladding layer to at least the firstface of the wedge-shaped light guide may comprise applying a liquid orgel-like cladding formulation to at least the first face and allowing atleast some of the liquid or gel-like cladding formulation to solidify.The liquid or gel-like cladding formulation may be chosen to have, aftercuring, a refractive index lower than that of the wedge-shaped lightguide. For example, the liquid or gel-like cladding formulation maycomprise a fluoropolymer dispersion or pre-polymerized fluoropolymerprecursor. Allowing at least some of the liquid or gel-like claddingformulation to solidify may comprise promoting a curingprocess—thermally or photochemically—as further described below. Inembodiments where a polymer precursor such as a fluoropolymer precursoris included in the cladding formulation, the solidification may comprisea polymerization or oligomerization process.

In some embodiments, the liquid or gel-like cladding formulation maycomprise a 100-percent-solids formulation; in other embodiments, theformulation may comprise a solvent or other vehicle to aid in dispersingthe cladding material or precursor.

In these and other embodiments, the liquid or gel-like claddingformulation may include an ultraviolet-curable component. Accordingly,method 100 may further comprise irradiating at least the first face ofthe wedge-shaped light guide with ultraviolet radiation to cure theultraviolet-curable component.

Depending on the particular liquid or gel-like cladding formulation inuse, various different modes of application may be used. In oneembodiment, the formulation may be sprayed onto at least the first faceof the wedge-shaped light guide in the form of an aerosol. In onevariant of this approach, the liquid or gel-like cladding formulationmay be dispersed ultrasonically during the spraying process.

In another embodiment, applying the liquid or gel-like claddingformulation may comprise at least partly immersing the wedge-shapedlight guide in the liquid cladding formulation, and, in some variants,withdrawing the wedge-shaped light guide from the liquid claddingformulation at an oblique angle with respect to a surface of the liquidcladding formulation. FIG. 20 shows an example application system 113 toenable a cladding to be applied to a wedge-shaped light guide 27 viaimmersion in, followed by withdrawal from, a liquid cladding formulation115. In one embodiment, the application system shown in the drawing maybe used with a liquid cladding formulation comprising a 2.5 percentsolution of MY-133MC (a product of MY Polymers), dissolved in a suitablesolvent. Suitable solvents include parachlorobenzotrifluoride (PCBTF),HFE-7100 (a product of 3M Corporation of Saint Paul, Minn.), andOxol-100 (a product of Halliburton Corporation of Houston, Tex.), forexample.

After immersion in the cladding formulation, the wedge-shaped lightguide may be withdrawn at an oblique angle with respect to the surfaceof the liquid cladding formulation—30 degrees, for example—using acontrolled-velocity, motorized lift. In this embodiment, the curing ofthe cladding layer may occur following, or at least partly during, thewithdrawal process. In some embodiments, immersion, withdrawal, andcuring may each be enacted once to provide a cladding layer of thedesired thickness. In other embodiments, repeated immersion and curingmay be used to attain the desired thickness.

In yet another embodiment, applying the liquid or gel-like claddingformulation may comprise applying the formulation to the first face ofthe wedge-shaped light guide in a fixed-thickness layer by dragging adoctor blade along and at a fixed distance above the first face.

Method 100 then advances to 114, where a turning film is adhered to thecladding layer via an interface layer. The turning film may comprise aprismatic patterned film to which broadband or dichroic reflectivecoating is applied, as described above. Applying the turning film viathe interface layer may comprise applying an adhesive layer to one orboth of the cladding layer and the turning film. The adhesive may bechosen such that the refractive index of the cured adhesive layer (i.e.,the interface layer) is matched to that of the wedge-shaped light guide.The turning film may then be compressed against the cladding layer. Insome embodiments, the adhesive may be a thermally curing resin—anepoxy/amine resin, for example. In other embodiments, the adhesive maybe air- or moisture-curing. In still other embodiments, the adhesive maybe ultraviolet-curing. It may comprise an ultraviolet-curing, acrylicresin, for example. Accordingly, method 100 may further compriseirradiating at least the first face of the optic with ultraviolet lightto cure the adhesive layer.

Method 100 then advances to 116, where any unwanted cladding layer isremoved from the wedge-shaped light guide. The unwanted cladding layermay be removed by chemical or mechanical etching, for example, byadhering a sticky film to the cladding layer and then lifting it off, orin any other suitable manner.

It will be understood that some of the process steps described and/orillustrated herein may in some embodiments be omitted without departingfrom the scope of this disclosure. Likewise, the indicated sequence ofthe process steps may not always be required to achieve the intendedresults, but is provided for ease of illustration and description. Oneor more of the illustrated actions, functions, or operations may beperformed repeatedly, depending on the particular strategy being used.

Finally, it will be understood that the systems and methods describedherein are exemplary in nature, and that these specific embodiments orexamples are not to be considered in a limiting sense, because numerousvariations are contemplated. Accordingly, the present disclosureincludes all novel and non-obvious combinations and sub-combinations ofthe various systems and methods disclosed herein, as well as any and allequivalents thereof.

1. A method for making an optic, the method comprising: forming awedge-shaped light guide having opposing first and second faces andcomprising a material having a first refractive index; applying acladding layer to the first face, the cladding layer having a secondrefractive index less than the first refractive index; and applying aninterface layer to the cladding layer opposite the first face, theinterface layer having a third refractive index matched to the firstrefractive index, wherein applying an interface layer to the claddinglayer comprises applying a turning film to the cladding layer via theinterface layer.
 2. The method of claim 1, wherein the first refractiveindex is 1.4 or greater.
 3. The method of claim 1, wherein the secondrefractive index is 1.4 or less.
 4. The method of claim 1, the opticconfigured to attenuate a reflection of light having a medianwavelength, wherein applying a cladding layer to the first facecomprises applying a cladding layer of a thickness corresponding to anodd-integer multiple of one-half of a selected median wavelength.
 5. Themethod of claim 1, wherein applying the turning film to the claddinglayer via the interface layer comprises applying an adhesive to one orboth of the cladding layer and the turning film, a refractive index ofthe adhesive being substantially equal, after curing, to the firstrefractive index.
 6. The method of claim 5, wherein the adhesive is anultraviolet-curing adhesive, the method further comprising irradiatingat least the first face with ultraviolet light to cure the adhesive. 7.The method of claim 5, wherein the adhesive is a polyacrylic adhesive.8. The method of claim 1, wherein applying the cladding layer to thefirst face comprises applying a moth-eye layer to the first face.
 9. Themethod of claim 1, wherein applying the cladding layer to the first facecomprises applying a liquid or gel-like cladding formulation to at leastthe first face and allowing at least some of the liquid or gel-likecladding formulation to solidify.
 10. The method of claim 9, wherein theliquid or gel-like cladding formulation comprises one or more of afluoropolymer dispersion, a fluoropolymer solution, and a fluoropolymerprecursor.
 11. The method of claim 9, wherein the liquid or gel-likecladding formulation comprises a 100-percent-solids formulation.
 12. Themethod of claim 9, wherein the liquid or gel-like cladding formulationcomprises an ultraviolet-curable component, the method furthercomprising irradiating at least the first face with ultravioletradiation to cure the ultraviolet-curable component.
 13. The method ofclaim 9, wherein applying the cladding layer to the first face comprisesapplying the liquid or gel-like cladding formulation to the first facein a fixed-thickness layer by dragging a doctor blade along and at afixed distance above the first face.
 14. The method of claim 9, whereinapplying the cladding layer to the first face comprises spraying aliquid or gel-like cladding formulation onto at least the first face.15. The method of claim 9, wherein applying the cladding layer to thefirst face comprises at least partly immersing the wedge-shaped lightguide in the liquid or gel-like cladding formulation, and, withdrawingthe wedge-shaped light guide from the liquid or gel-like claddingformulation at an oblique angle with respect to a surface of the liquidor gel-like cladding formulation.
 16. A method for making an optic, themethod comprising: forming a wedge-shaped light guide having opposingfirst and second faces and comprising a material having a firstrefractive index; spraying a liquid or gel-like cladding formulationonto at least the first face and allowing at least some of the liquid orgel-like cladding formulation to solidify, the liquid or gel-likecladding formulation, after curing, having a second refractive indexless than the first refractive index; and applying a turning film to thecladding layer via an interface layer, the interface layer having athird refractive index matched to the first refractive index.
 17. Themethod of claim 16, further comprising dispersing one or more componentsof the liquid or gel-like cladding formulation ultrasonically whilespraying.
 18. A method for making an optic, the method comprising:forming a wedge-shaped light guide having opposing first and secondfaces and comprising a material having a first refractive index; atleast partly immersing the wedge-shaped light guide in the liquid orgel-like cladding formulation and allowing at least some of the liquidor gel-like cladding formulation to solidify, the liquid or gel-likecladding formulation, after curing, having a second refractive indexless than the first refractive index; and applying a turning film to thecladding layer via an interface layer, the interface layer having athird refractive index matched to the first refractive index; whereinapplying the cladding layer to the first face comprises applying aliquid or gel-like cladding formulation to at least the first face. 19.The method of claim 18, further comprising withdrawing the wedge-shapedlight guide from the liquid or gel-like cladding formulation at anoblique angle with respect to a surface of the liquid or gel-likecladding formulation.